The effects of low-velocity layer and basin topography on near-field ground motion amplification

Near-field ground motion amplification in sedimentary basins is widely observed and crucial to earthquake hazard assessment. However, the effects of basin topography coupled with the low-velocity layer (LVL) on ground motion amplification are not fully understood. By constructing 3D basin models with surrounding mountain terrains and performing ground motion simulations, we compare the ground motion characteristics with different basin LVL depths and LVL velocities. The velocity contrast between the LVL and bedrock controls the amplification magnitude. The maximum amplification area in the model changes from the central part to the periphery part of the basin as the velocity contrast decreases and can be greatly influenced by the distance between the source and the basin. The amplification also spreads along the mountain edge circling the basin. Our work sheds light on the distribution of amplification within sedimentary basins surrounded by mountains, revealing that the velocity contrast between the LVL and bedrock plays a pivotal role in controlling the magnitude of amplification.